The present disclosure relates to a hydrocyclone for separating a fiber suspension into a reject fraction substantially containing heavy contaminants and an accept fraction substantially containing fibers, comprising a housing with a circumferential wall defining an elongated separation chamber with two opposite ends and with a center axis extending between the opposite ends. The hydrocyclone further comprises an inlet member for supplying the fiber suspension substantially tangentially into the separation chamber at one end thereof, so that the fiber suspension flows in a vortex in the separation chamber, a first outlet member for discharging the accepts fraction from the separation chamber at said one end, and a second outlet member for discharging the rejects fraction from the separation chamber at the other end thereof, and a distribution head for supplying a fluid to the separation chamber.    The '153 System:
An example of a conventional system can be found in US Published Application 2006/0163153 (the '153 system), which is incorporated herein in its entirety by reference. A portion of that description is reproduced below, and like numbers for similar items are used in all of the drawings.
The '153 system is described in more detail in the following drawings, in which FIG. 1 shows a view of an axial cross-section through a hydrocyclone, FIG. 2 shows an enlarged fluid supply device in the hydrocyclone according to FIG. 1, FIG. 3 shows a cross-section along the line III-III in FIG. 2, and FIG. 4 shows a modification of the embodiment according to FIG. 3.
In FIG. 1 there is shown an example of a hydrocyclone 2 according to the '153 system, specially dimensioned for separating a fiber suspension containing relatively light and heavy contaminants. The hydrocyclone 2 comprises a housing 4, which forms a separation chamber 6, which is 49 cm in length, with a circumferential wall 8. The separation chamber 6 has a conical chamber section 10, and a cylindrical chamber section 12 connecting the base of the conical chamber section 10, whereby the separation chamber 6 has a relatively broad base end 14 and an opposite relatively narrow open apex end 16.
There is an inlet member 18 for supplying the fiber suspension tangentially into the cylindrical chamber section 12 at the base end 14 of the separation chamber. A first outlet member in the form of a pipe 20 extends centrally a distance into the cylindrical chamber section 12 from the base end 14 of the separation chamber 6 for discharging a light fraction of fiber suspension substantially containing fibers. A second outlet member 22 is arranged at the apex end 16 of the separation chamber 6 for discharging a heavy fraction of the fiber suspension containing heavy contamination particles, such as sand, metal fragments and the like. A third outlet member in the form of a pipe 24 having a substantially smaller diameter than the pipe 20 extends centrally through the pipe 20 for discharging a further light fraction of the fiber suspension containing light contamination particles, such as plastic fragments and the like.
The hydrocyclone 1 further comprises a fluid supply device 26 for supplying liquid and/or gas to the conical chamber section 10 of the separation chamber 6 relatively close to the apex end 16. The fluid supply device 26 comprises a supply pipe 28 attached to a cylindrical plug 30 secured in the apex end 16 of the separation chamber 6. The circumferential wall 8 passes from the apex end 16 to a radially expanded portion 32 of the housing 4, which defines an open cylindrical chamber 34, which is closed by the plug 30, for example through threads, so that the supply pipe 28 extends centrally into the conical chamber section 10 via the apex end 16. The end of the supply pipe 28 in the separation chamber 6 is closed by a distribution head 36, which comprises a cylindrical wall 38 with two axial ends and a gable wall 40 covering one end of the wall 38 (see FIG. 2).
The wall 38 is provided with three radial bores forming outlet passages 42, which communicate with the interior of the supply pipe 28 (see FIG. 3). In this case, each outlet passage 42 opens in the conical chamber section 10 about 4 cm from the apex end 16. The distribution head 36 and the circumferential wall 8 of the conical chamber section 10 define an annular passage 44 for developed heavy fraction, the passage 44 having a radial extension of about 0.5 cm.
During operation of the hydrocyclone 1 according to FIG. 1, the fiber suspension, which contains relatively light and heavy contaminants, is pumped by a pump 50 tangentially into the separation chamber 6 via the inlet member 18, so that a vortex of the fiber suspension is created in the separation chamber 6. As a result, the fiber suspension separates into an accepts fraction substantially containing fibers, which are discharged through the pipe 20, and a reject fraction containing relatively heavy contaminants, which are discharged through the outlet member 22. A mixture of water and air is sprayed by the fluid supply device 26 against the circumferential wall 8 of the conical chamber section 10 to dilute the developed thick heavy fraction and release embedded fibers, so that these may follow the developed light fiber fraction. The injected air separates in the form of bubbles inwardly in the separation chamber 6 and entrains light contaminants to the centrally situated pipe 24.
Of course, as an alternative, the fluid supply device 26 may only supply liquid or gas to the separation chamber 6.    Problem
A well-known problem that might arise during operation of hydrocyclones of this kind is that the heavy fraction, which typically has a substantially smaller flow than the light fiber fraction, thickens heavily and as a result might tend to clog. This problem is reduced by supplying the fluid in the form of liquid to the separation chamber in order to dilute the thickening heavy fraction.
The usage of a dilution device in hydrocyclone separation is today very common and installed on most cleaner plants in order to primarily minimize the loss of good fiber in the reject.
The existing designs offered to the pulp industry of the diluting devices that reduce fiber packing (or other insoluble particles) show problems during operation of the hydrocyclone.